Malaria is an infectious disease that is caused by malaria parasites mediated by anopheles. Since recorded history, malaria has been the infectious disease most feared by humans mainly in the tropical and subtropical regions. A decrease in the number of malaria-infected people has been temporarily observed because of specific drugs such as quinine and chloroquine. Since the late 1950s, however, drug-resistant parasites have been discovered, and even nowadays, 300 to 500 million people per year are infected with malaria parasites as a reemerging infectious disease. It is said that 1 to 2 million people die from malaria every year. Many other infectious diseases are treated or prevented by vaccination. For example, smallpox was completely eradicated. In the case of malaria, however, since it is an infection caused by parasites, or since the parasites have a complicated life cycle, even a key for the development of a vaccine has not yet been found, although many studies have been conducted. It is said that it may be essentially difficult to develop a vaccine used for malaria.
Many studies have been conducted regarding the development of new drugs or the mechanism of drug resistance. On the other hand, parasites which have developed resistance to drugs have been successively found. Hence, we are facing a crisis. In general, existing antimalarial drugs have strong side effects, and thus these drugs cannot be used in a preventive manner in an area in which malaria is spread. In addition, enormous costs are required for the development of a new drug, and therefore such drug development brings on a serious economic problem.
Conventionally, as a therapeutic method, photodynamic therapy (PDT therapy) has been known. PDT therapy is a treatment method involving combining a photosensitizer with light irradiation. ALA does not have photosensitizing properties by itself. However, since ALA is metabolized to the photosensitizing substance protoporphyrin IX (PPIX) in the body, it is used in the PDT therapy for cancer (see, for example, patent documents 1 to 3). For the PDT therapeutic method using ALA, studies have been conducted on a petri dish using malaria parasites (see, for example, non-patent document 1). PDT therapy certainly exhibited effects on malaria. However, in order for PDT therapy to exhibit some effect by illumination with ordinary indoor light, as much as 2 mM of ALA needs to be added to a medium. It means that at least 20 g of ALA hydrochloride needs to be administered to a person weighing 60 kg, and that it is impossible to administer ALA in such an amount because of a toxicity problem. In order to obtain a sufficient parasiticidal effect when ALA was added to a medium in a concentration of 0.2 mM corresponding to 2 g, that is twice the dosage which general human bodies can tolerate, light irradiation from a strong projector lamp of 410 W for as long as 30 minutes was necessary. These resulted from tests using a transparent medium on a petri dish, and light transmission properties were high. In reality, however, since malaria parasites are parasitic in erythrocytes in the blood, light irradiation is unrealistic, and subsequent studies have not progressed yet.
Moreover, a hair restorer containing ALA and an iron compound as active ingredients (see, for example, patent document 4) and a drug for preventing and/or improving skin roughness (see, for example, patent document 5) have been proposed.